Method of stirring materials and apparatus therefor

ABSTRACT

A method of stirring to mix a liquid material with another material, such as another fluid (liquid or gas) or a finely divided solid, in a container. A circulation of the materials is generated within the container between one container end and the other end of the container, which is at least equal to the diameter of the first end. A circulating force is imparted to the materials at the first end of the container to create a limited throughflow with a helical peripheral component creating a negative pressure at the center of the first end of the container producing an external flow of materials in an outer zone rotating along the wall of the container from the first end to the second end of the container. Near the second end a substantial part of the spin from the external flow at the second end is removed to produce a higher static pressure at the center of the second end than at the center of the first end, to establish an internal laminar flow of materials from the second end to said first end, which is substantially parallel to the external flow and exceeds the maximum diameter of the confined material flow path. Between the oppositely moving inner and outer paths of material flow, an annular elongate zone of turbulence is generated to create efficient mixing of the materials. The disclosure shows several embodiments of a stirring container apparatus to accomplish mixing between parallel zones of oppositely moving material; namely a container having a base at one end, a cover closing the other end, a liquid driving or circulating unit including an impeller within the container at one end, e.g. the base end. The impeller is shaped to cause material flow leaving the impeller to follow a path adjacent the base wall to the adjoining container wall and then along the container wall with a spin or spiralling flow to the other end of the container where vanes remove the spin and the material flow is reversed at the cover end to pass back along the center of the container. The diameter of the cover end is at least equal to and preferably greater than the base end and the length of the interior space of the container exceeds the maximum interior diameter of the container. The container walls between the base and cover should be smooth and either cylindrical or frusto-conical, preferably the latter for most efficient operation.

' 22 Filed:

United States Patent Schoppe [54] METHOD OF STIRRING MATERIALS ANDAPPARATUS THEREFOR [72] Inventor: Fritz Schoppe, 8026 Ebenhausen/Isartel Max Ruttgers, Strs. 24,

M sh fl y Oct. 1, 1969 [21] Appl. No.: 862,744

[30] Foreign Application Priority Data Primary Examiner-Jordan FranklinAssistant Examiner--Geo. V. Larkin Attorney-Strauch, Nolan, Neale, Nies& Kurz 5 7] ABSTRACT A method of stirring to mix a liquid material withanother material, such as another fluid (liquid or gas) or a finelydivided s olid, in a container. A circulation of the materials isgenerated within the container 0 between one container end and the otherend of the "[4s1 Aug. 22, 1972 container, which is at least equal to thediameter of the. first end; A circulating force is imparted to thematerials at the first end of the container to create a limitedthroughflow with a helical peripheral component creating a negativepressure at the center of the first end of the container producing anexternal flow of materials in an outer zone rotating along the wall ofthe container from the first end to the second end of the container.Near the second end a substantial part of the spin from the externalflow at the second end is removed to produce a higher static pressure atthe center of the second end than at the center of the first end, toestablish an internal laminar flow of materials from the second end tosaid first end, which is substantially parallel to the external flow andexceeds the maximum diameter of the confined material flow path. Betweenthe oppositely moving inner and outer paths of material flow, an annularelongate zone of turbulence is generated to create efficient mixing ofthe materials. The disclosure shows several embodiments of a stirringcontainer apparatus to accomplish mixing between parallel zones ofoppositely moving material; namely a container having a base at one end,a cover closing the other end, a liquid driving or circulating unitincluding an impeller within the container at one end, e.g. the baseend. The impeller is shaped to cause material flow leaving the impeller,to follow a path adjacent the base wall to the adjoining container walland then along the container wall with a spin or v spiralling flow tothe other end of the container where vanes remove the spin and thematerial flow is reversed at the cover end to pass back along thecenterof the container. The diameter of the cover end is at least equal to andpreferably greater than the base end and the length of the interiorspace of the container exceeds the maximum interior diameter of v thecontainer. The container walls between the base and cover should besmooth and either cylindrical or frusto-conical, preferably the latterfor most efficient operation.

19 Claims, 9 Drawing Figures PATENTED M1922 I972 SHEET10F3 Fig. I

INVENTOR FRITZ SCHOPPE ATTORN EYS PATENTEDmszz 1972 SHEET 2 [IF 3INVENTOR FRITZ SCHOPPE ATTORN EYS PATENTED M22 1972 sum 3 or 3 INVENTORFRITZ SCHOPPE BY f 7.4

ATTORNEYS METHOD OF STIRRING MATERIALS AND APPARATUS THEREFORCylindrical stirring apparatus containers are known in which there issituated a stirring tool for mixing a liquid with another substance,and, if desired with the supply and discharge of heat. The stirring toolis driven by a central rotating shaft and has the form of a propeller,or of crossed arms or a similar form suitable for mixing liquids.

Detailed studies, carried out within the course of extensiveexperiments, of the mixing processes in known stirring apparatuscontainers have shown that, not only in the case of liquids of lowviscosity, but also in the case of liquids of medium or high viscosity,the whirling of the liquid, i.e. the turbulent exchange processes ofmomentum, matter and heat, have a determining effect even when, in thecase of liquids of relatively high viscosity, the final fine mixing iseffected only by intermolecular processes, for example diffusion or heatconduction. The method and stirring apparatus can be used to homogenizethe water and other chemicals of milk with the fatty materials of creamor to mix the oils and pigments of paints or to mix chemicals forplasticizers as well as mixing many other materials.

Further investigations had the object of finding a direct measure of theeffectiveness of a mixing process. It was found that the range ofturbulent fluctuation frequencies which arises in a turbulent flow is adirect measure of the mixing performance. By turbulent fluctuationfrequencies is meant the following.

In any turbulent flow, there exist large and small vortices. With agiven speed of rotation, the large vortices have a low rotationalfrequency, while the small vortices have a high rotational frequency. Ifthere are many large vortices, the components to be mixed are broughttogether from a long distance, while the small vortices ensure the finalfine mixing. From the viewpoints of measuring technique and mathematics,it is simpler to consider the reciprocal of the vortex diameter, i.e.the whirling frequency. It is therefore obvious that a mixing processproceeds more intensively in proportion as the range of high and lowfrequencies in the liquid is greater. This range is known as theturbulence spectrum or the range of excited turbulent fluctuationfrequencies.

It is also known that this range depends upon the manner in which theturbulence is produced. In. all known stirrers, there are set up, inaddition to a rota- ,tion about the axis of the stirrer, rotationalmovements of the most varied kinds in radial planes. If, for example,the stirrer has the form of a propeller, the propeller will accelerate aliquid stream in an axial direction, for example downwardly. Parts ofthe liquid consequently flow upwards in the neighborhood of the wall,are reversed inwardly towards the axis of the stirrer at the top andthen tend to flow downwards towards the propeller again.

In other stirrer constructions, resistance bodies, for example such ascrossed arms, blades or anchor-shaped arms, are moved by the liquid.Beyond these resistance bodies, the flow is detached in known manner andalso forms rotating vortices of the most varied forms, which, accordingto the form of the stirrer, rotate in different planes and may havesuperimposed upon them other rotational and throughflow motions.

In any case, however, clearly determinable rotating flow elements exist,closer investigations having shown that the velocity distribution in theexternal regions of the rotating zone corresponds substantially to apotential vortex, while there exist in the interior partly rotationalmovements having a constant angular velocity,

and partly completely random motions. These zones of rotationgenerallyalso known as vortices-have only a limited lifetime owing to their flowlosses in the internal region and thereafter break up into smallervortices, whereby they produce the mixing process.

All these flows have like turbulence spectra, assuming comparabledimensions and speeds of flow. More especially, a relatively highReynolds number is required in order to obtain turbulence at all. As isknown, laminar and therefore nonturbulent flow exists below thisReynolds number.- As the Reynolds number increases, the turbulencespectrum initially widens, but thereafter narrows again. At very'highReynolds numbers, the turbulence spectrum returns towards zero. Thisfact is also known from the boundarylayer theory.

The aforesaid conditions are always obtained provided that the saidrotating individual vortices occur in the flow, and zones of intensivemixing and zones of less intensive mixing are then produced.

The object of the invention is to provide'a method of mixing liquids ina stirring apparatus container,

wherein zones of less intensive mixing are substantially avoided, sothat the intensity of the mixing can be considerably increased and themixing performance thus greatly enhanced.

In accordance with the invention, the aforesaid object is achieved byvirtue of the fact that, for producing an external flow rotating alongthe inside walls of the stirring apparatus container from the first endof the latter to the second end, there is imparted to the material to bemixed, in the region of the first end of the container, a limitedthroughflow and peripheral component with maximum negative pressure inthe center of the first container end, and by virtue of the fact that,for producing a higher static pressure at the center of the second endofthe container than at the center of the first end of the container, asubstantial part of the spin is extracted from the external flow closeto the wall, in the region of the second end of the container, therebeing set up an internal flow which is substantially parallel to theexternal flow and which extends over a sufficiently long distance of atleast 5 to 6 times and preferably 10 to 12 times the thickness of eachindividual flow layer in the region of the longitudinal axis of thecontainer, from the second end of the latter to the first end thereof,the velocity of the said internal flow being of equal order of magnitudebut of opposite direction to the said external flow, while an elongatetubular zone of intensive turbulence is developed between the externalflow closed to the wall and the oppositely flowing central internalflow.

Further advantageous developments of the method of the invention will beapparent from the following description and from the claims.

By means of the method of the invention, there is produced in a stirringapparatus container a very particularly flow pattern, in which thereexist completely different conditions from those of flow patternsarising in the known stirring apparatus containers. If it is enthemanner of a short circuit.

sured that as far as possible no flow short-circuits are formed in theflow pattern produced in accordance with the invention, i.e. that eachflow actually passes through the wholelength of travel, no rotatingindividual vortices are developed in a stirring apparatus containeroperated in accordance with the invention,

the entire surface of separation and thus also produces a hithertounattained intensivemixing,

The turbulence spectrumobtained by the method of the invention is thusof fundamentally different appearance fromthat obtainedin the operationof known stirring apparatus containers.

It is found that the turbulence of the method of the invention commencesat a very much lower critical Reynolds number. This Reynolds number islower substantially by a'factor. of.25 than in the case of the Inaccordance with the invention, the rotation of the outside flow shouldbe only just sufficiently strong to.

keep the flow against the wall'by'centrifugal force. If the rotationcomponents were too high in relation to the throughflow component,centrifugal effects would be set up asin a cyclone separator, whichwould be so great as to cause a separation of matter and not aninterrnixing.

On the other hand, in order to cause the opposed flow to take place fromthe second end of the container to the first end thereof along itsaxis,there must be made available to this flow in accordance with thein- I vention a pressure gradient such as to ensure that it aforesaidcontainers. With comparableReynolds numbers, the turbulence spectrumobtained in accordance with the invention, i.e. the range of excitedturbulent fluctuation motions, and thus also the specific mixingperformance, is about 4 to 6 times greater, depending upon thecomparison basis. At higher Reynolds numbers, the turbulence spectrumtends towards zero in the known procedures, but in a procedure accordingto the invention the turbulence spectrum proceeds asymptotically towardsa constant value, The turbulence produced in accordance withtheinvention occurs even at'low and medium Reynolds numbers and islargely independent of the Reynolds number provided that a very lowcritical Reynolds number is exceeded.

' The frequency spectrum produced in accordance with the inventionresults in an increased momentum exchange and thus'in a greater flowfriction. However, since any flow tends to proceed along the path oflower resistance, each of the opposed flow. components would initiallyexhibit a tendency towards flow shortcircuits. Such flow short-circuitsmay be avoided in accordance with the invention by applying to the twoopposed flows additional forces which are sufficiently high in relationto the local pressure heads.

' Y Such additional forces may most simply be produced in a rotationallysymmetrical stirring apparatus container.

For example, in an elongate cylindrical or conical container employed inaccordance with the invention, there may be produced a flow close to thewall, which proceeds from the first end to the other, second end, whilethere exists in the region of the axis of the container an opposed flowwhich proceeds fromthe second end back to the first end. If a certainrotation,

which is as weak as possible, is imparted to the outside flow inaccordance with the invention, it in fact travels from the firstcontainer end to the second without flowing to the center, immediatelyafter leaving the, first end of the container, and then back to thesaid' first end in flows from the second end of the container to thefirst. This pressure gradient may be produced by extracting the spin tothe-greatest possible extentfrorn' the flow component close to the wallby means of a guide device as soon as itreaches the second end of thecontainer. lf this were not done, the flow close to the wall would flowinwardly towards the axis at the second end of the container and wouldacquire a high peripheral velocity in accordance with the spin theorem.According to Bernoullis theorem, the static pressure would thusdecrease, and .this is not desired in accordance with the I invention.On the contrary, in accordancewith the invention, a maximum staticpressure mustobtain-at the center of the cross-section at the second endof the a container in order that a pressure gradient may be present fromthe center of the. second end of the container to the center of thefirst-mentioned end of the container. f

In order to produce a sufficiently high negative pressure at the centerof the cross-section of the first endof the container, it is possible inaccordance with the invention to provide at the first end of thecontainer an impeller of the type employed in centrifugal pumps, ofwhich thecentral intake aperture is directed towards the second end ofthe container. The flow is then thrown radially outwards and directed onto the outside wall of the container in order that it-rnay flow -with amoderate peripheral component towards the second endof the container toform a flow pattern according to the invention. r

lnaccordance with the invention, the impeller at the desired course ofthe flow in the container by providing 1 it with a relatively largeintake aperture, while the out-.

let cross-section 'inthe neighborhood of the wall extends only over arelatively small part ofthe external diameter, because the centralreturn flow directed from the second end of the container to the firstend thereof advantageously occupies substantially the inner percent ofthe diameter of the container, while the flow close to the wall from thefirst-mentioned end of the container to the other end has a layerthickness of only about 10-20 percent of the diameter of the container.

This is due substantially to the fact that, in the first place,the'cross-section depends on the square of the diameter, and in'thesecond place to the fact that the velocity profile of the flow close tothewall has a somewhat different form from that ,of the central returnflow, the flow close to the wall having a somewhat higher maximumvelocity value thanthe return flow.

Independently thereof, however, there is formed between the two flows inaccordance with the invention a tubular zone of very intensiveturbulence, which fills the whole container with the exception of theboundary layer close to the wall. It is only in the boundary layer closeto the wall that no turbulence i.e. i.e., no radially directed flowcomponents are present.

In accordance with the invention, it is advantageous to cover theimpeller between the intake cross-section and the outlet cross-sectionin known manner in order thus to effect a better guiding of the flow.

For increasing the pressure gradient of the central return flow, it isdesirable in accordance with the invention to widen the container in thedirection from the first end of the container to the second end. Due tothis widening, the peripheral velocities decrease in accordance with thespin theorem and the static pressures correspondingly increase. Thestatic pressure at the center of the second end of the container alsocorrespondingly increases, whereby the pressure gradient along the axisof the container, from the second end of the latter to the inletcross-section of the impeller, is increased. In a container thusconstructed and employed in accordance with the invention, the mixingperformance per unit volume is about 4-6 times as great as in otherstirrers known at present. Moreover, the turbulence commences atsubstantially lower Reynolds numbers, so that it is possible to produceturbulence in substantially more highly viscous liquids than in knownstirring apparatus containers. In addition, in the method of theinvention, the turbulence spectra, and thus the flow patterns above acertain, relatively low Reynolds number are no longer dependent upon thelatter, and the flow patterns become modular with sufficient accuracyfor practical purposes. The invention consequently affords thepossibility of removing any desired quantities from liquid stirrers andof accurately predetermining the efficiency of the mixing process, asalso the necessary driving energies.

The fact that the tubular turbulence zone produced in accordance withthe invention has a more or less strong peripheral componentsuperimposed thereon owing to the general rotation of the liquid hasonly negligible effect on the efiiciency of the mixing process.

A stirring apparatus container for carrying out the method of theinvention, consisting of a conical or even cylindrical container havinga base and a cover, as also a driving unit rotating about the base is soconstructed in accordance with the invention that the driving unit hasthe form of an impeller of a centrifugal pump, which impeller isprovided with conveyor blades which are so shaped that the flow leavingthe impeller is adapted to the form of the base and of the adjoiningcontainer wall, while the axial length of the container is greater thanits maximum diameter.

As preferred embodiments of the apparatus of this invention there arediagrammatically illustrated in FIGS. 1 to 8 of the drawings a number ofadvantageous forms of construction of the stirring apparatus containeraccording to the invention, which will hereinafter be more fullydescribed and the particular manner of operation of which will beexplained. In the drawings:

FIGS. 1 to 4 are longitudinalsections through four different stirringapparatus containers according to the invention.

FIG. 5 is a longitudinal section through a stirring apparatus container(drawn to a larger scale).

FIG. 6 is a longitudinal section through a further stirring apparatuscontainer,

' FIG. 7 is a cross-section through the stirring apparatus containeraccording to FIG. 6 along the line VIIVII,

FIG. 8 is a cross-section through the stirring apparatus containeraccording to FIG. 6 along the line VIII-VIII, and I FIG. 9 is alongitudinal section through a further different shape of stirringapparatus according to the invention.

In the drawings, corresponding parts of the stirring apparatuscontainers are i denoted by the same reference numerals.

As is apparent from FIG. 1, a stirring apparatus container according tothe invention consists of a conical container 1 having a base 2 and anupper cover 3. Rotating in the neighborhood of the base 2 is acentrifugal pumptype impeller consisting of a supporting shell 4corresponding to the shape of the base, which shell is rotated by meansof a shaft 5 and supports known conveyor blades 6. Situated at theopposite end of the container 1 are fixed guide vanes 7 which extractthe twist from the flow. The components to be mixed are supplied throughconnecting pipes 8 and 9 which may also serve as air extraction and gasextraction pipes. A discharge duct 10 is employed for emptying.

On rotation of the impeller 4,5,6, it acts as a centrifugal pump andconveys the flow with a moderate twist along the walls of the container1 to the opposite end of the container. At this end, the fixed guidevanes 7 extract the spin from the rotating flow, whereby a substantiallyequal static pressure is set up over the whole cross-section in theregion of the guide vanes 7. From here, the impeller sucks in itsthroughflow along the axis of the container 1, so that two flowcomponents are set up, namely one flow from the region of the center ofthe guide vanes 7 along the chamber axis to the inlet of the impeller,and a second flow, on which a weak rotation is superimposed, from theoutlet of the conveyor blades 6 into the guide vanes 7. This flowpattern according to the invention has in fact theoretically predictedproperties of increased specific mixing performance.

FIG. 2 illustrates a second form of construction of the stirringapparatuscontainer according to the invention, wherein the shaft 5 doesnot extend from the bottom through the base 2, but is introduced intothe container from the top through the cover 3. This may af-- fordadvantages when solids or other corrosive components may impair thestufling box for the passage of the shaft 5 through the base 2.

FIG. 3 illustrates a further variant of the stirring apparatus containeraccording to the invention, in which there are provided instead ofsimple radial guide vanes 7, guide vanes having a flow-favoring form,which extend around the ring 11 of packing material in order that anorderly flow may take place around the latter. With such a device, andwith an appropriate form of the guide vanes 7 in accordance with theknown rules of centrifugal pump construction, additional economies indriving energy may be effected.

FIG. 4 illustrates another form of construction of the container 1,which in this case is not conical, but cylindrical. This has theadvantage of simplifying manufac- -ture, but it has the disadvantagethat the pressure gradient of the return flow from the guide vanes 7 tothe impeller at the opposite end is weaker. The specific mixingperformance is also correspondingly lower..

apertures 12 which efiect a certain throughput of liquid through theclearance between the supporting shell 4 and the base 2, which isthereby flushed clear.

In addition, the conveyor blades 6 may be covered by a ring-shaped guidebody 13 which imparts to the issuing flow a direction corresponding tothe adjoining out side walls and on the other hand directs the axialreturn flow to the inlet edge of the conveyor blades 6.

vWhen the container is sufficiently filled, it' is immaterial in whatposition the apparatus is disposed. Thus, it may lie on its side or itmay be inverted. The functions of the air extraction ducts, the supplypipes and the discharge pipes are then changed accordingly.

The invention covers all of the constructional features referred to. i

The flow pattern in a stirring apparatus container according to theinvention is independent of the Reynolds number, i.e. independent ofthe-dimensions, the flow velocity and the viscosity of the liquid,provided that the Reynolds number exceeds certain minimum values. Thespecific mixing performances of small and large apparatus are thereforeequal. For this' reason, only relative particulars need be given for optmum configurations. i

It has proved particularly desirable to make the container .l conical,in which-case the larger diameter of the container 1 is twice as largeas the small diameter of the conical container 1, whilethe axial lengthof the container 1 is 3.5 times the small diameter. This corresponds toa configuration according to FIG. 1. a In the case of a cylindricalconstruction according to mixing performance is low. On deviation fromthe op I timum values-of the ratio of length to diameter towards thevalue 121, the specific mixing performance correspondingly decreases,whilethe energy consumption and the mixing time increase. V

The base 2 and theother end or cover 3 have in the optimum case the formof a segment of a sphere or of a basket-handle or segmental arch.Somewhat less favorable is the shape of a cone, which in the boundarycase may degenerate to a flat base, but this is the least favorable fromthe viewpoint of strength and flow technique.

. The final conceivable configuration in which the base 2 has alargerdiameter thecov er 3, i.e. in which the container 1 has theinverse conicityof that'in FIG. 1, is evenless favorable from theviewpoint-of mixing efficiency than the cylindrical shape according toFIG. 4. In the case of the inverted conicity, the

diameters decrease with increasingdistance fro'm'the I impeller;according to thespin. theorem, the peripheral components of the flowcorrespondingly increase. Ac-

FIG. 4, which represents the limit case of the conical not well beutilized, because the velocities in that part;

of the container which is at the opposite end to the impeller are lowand the mixing thereat is correspondingly lower; t

. 'Whenthe optimum ratio of length to diameter is exceeded, theintensity of the tubular turbulence zone constantly decreases; astheorder of magnitude of the ratio of length to diameter 1:1 isapproached, the

throughfiow components form a toroidal vortex ring,

.' the tubularturbulence zone becoming a torus whose cording toBemoullis theorem, the static pressures thus decrease, and hencethe-pressure gradient which drives the return flow is weakened along theaxis of the,

container 1 in the direction of the impeller. As. the return flowbecomes weaker, the mixing also becomes less efficient. i l

Intermediate forms between the conical form according to FIG. 1 which ismost favorable for the'flow,

and the simplified cylindrical form according to FIG. 4

are also conceivable, e.g., assho'wn in FIG. 9 wherein the internalcontour 31 is' composed of at least one conical part 32 and onecylindrical part 33, which, in-

volves lower manufacturing cost than a purelyconical container, but thespecific'mixing performance of which lies between that of the purelyconical form and that of the purely cylindrical form. In. theintermediate form of "FIG. 9 the shaft 34 is shown extending through thecover 35 down to the impeller constituting support shell 36 and impellervanes 37 located at the base end 38 in a manner like that described forFIG. 2. Other components, such as the pipes 8 and 9', the fixedstationary) guide vanes 7' and the discharge duct 10' are similar inlocationgand function. to the corresponding components described forFIGS. 1-4.

FIG. 6. illustrates in greater detail a stirring apparatus containeraccording to the invention which consists of f a conically wideningcontainer part 1, a flanged-on lower base portion 2 and an upper cover3, which is fix-- edly connected to a connecting pipe 8 which extendscentrally into the container 1 substantially to the level of the fixedguide vanes 7. The guide vanes 7 consist of radial sheet-metal sections(FIG. 7) which arewelded to aring-shaped body 7 disposed centrallyin'the con tainer l and extend as far as and are fixed to the insidewall of the container 1, which extends inwards in pear l shape above theguide vanes and adjoins a centrally situatedcylindrical end portion 14with a flange 15 for receiving the cover 3. A connecting pipe 9, whichmay serve as an air extraction and gas extraction pipe, opens into theend portion 14 i There extends into the base portion 2 an blades 6,which are covered by a ring-shaped guide being welded to the conveyorblades.

impeller which consistsof a supporting shell 4 having conveyor Theradially outwardly extending conveyor blades 6 are bent over out oftheir radial direction in scoop-like form in the region of the guidebody (FIG. 8). Engaging centrally with the base of the supporting shell4 is a tubular-shaft 16 which serves for connection of the impeller to ashaft 17, which is adapted to be driven by a motor 19 through gearing(not shown) in a housing 18. The shaft 17 with the tube 16 engagingaround it is covered by a cylindrical intermediate housing member 20,which is flanged on the one hand to the gear housing 18 and on the otherhand to the container base portion 2. The upper end of housing member 20is shaped as a stepped flange ring 21 which fits into the container baseportion 2 and comprises at its forward end, conically inwardly extendinginclined surfaces 22 with packing rings 23. When the apparatus is readyfor operation, bevelled shoulders 24 on the rear face of the dishedsupporting plate are lifted from the inclined surfaces 22. For packingthe passage of the shaft 17 through the bottom of the base portion 2,there are provided a packing ring 25 and an adjoining stuffing box 26,which is held in its packing position by an assembly ring 27. Thepacking ring 25 and a portion of the stuffing box lie between the insidesurfaces of the flange ring 21 and the outside surfaces of the tube 16.For removing the packing 25,26, the motor 19 can be downwardly withdrawnwith the gearing l8 and the shaft 17. The supporting plate.4 of theimpeller thus bears in fluid-tight manner at its shoulders 24 on thepacking rings 23 at the inclined surfaces 22 of the flange 21, so thaton replacement of the packing 25,26 the liquid need not be drained fromthe container.

For draining off the liquid, the base portion 2 is provided in its lowerregion with a branch pipe 28. The guide body 13 may consist of a hollowring-shaped body.

I claim:

1. A method of mixing a liquid material with another material, such asanother liquid, a gas, or a particulate solid, in a container in whichthe materials are circulated between a first end of the container and asecond end of the container, the diameter of the second end being atleast equal to the diameter of the first end, comprising: imparting tothe materials within the container and at the first container end alimited throughflow with a peripheral spin component and having amaximum negative pressure at the center of the first end of thecontainer so as to produce an outer flow path zone of materials rotatingalong the inside surface of the wall of the container from the first endto the second end of the container, extracting a substantial part of thespin from the outer zone of flow at the second end providing asubstantially straight nonspinning flow to produce a higher staticpressure at the center of the second end than said maximum negativepressure at the center of the first end, thereby establishing an innerflow path of materials within said outer zone passing from said secondend to said first end which is substantially parallel to the outer zoneof flow, the interface between the opposite flow paths creating anannular turbulent elongate zone of mixing of the materials.

2. A method according to claim 1, wherein the inner flow path extendsover a sufficiently long distance of at least five times the thicknessof each individual flow layer adjacent the longitudinal axis of thecontainer,

- rotating centrifugal-type pump impeller disposed cenand the velocityof said inner flow is of equal order of magnitude but of oppositedirection to the velocity of the outer zone of flow.

3. The method according to claim 2, wherein the inner flow extends overa distance of about ten to twelve times the thickness of each individualflow layer in the region of the longitudinal axis of the container.

4. The method according to claim 1,- wherein the diameter of the secondcontainer end is greater than the diameter of the first container endand the outer zone of flow of materials moves in a conically wideningpath from the first end to the second end.

5. A method according to claim 1, wherein material from the inner flowis sucked into the inlet opening of a v cover at itsother end; and aliquid and material driving unit including a rotating impeller meanspositioned closely adjacent said base end; said impeller means havingblade support means and a plurality of radially directed blade meanssecured to saidblade support means, said blade means having outletportions disposed in a direction away from said base end and with saidsupport means enabling flow of material leaving said impeller means,when rotating, to flow outward at the base end and directed toward andalong the adjoining container wall toward said other' end whileproviding a rotational component in the flow path along the containerwall, .and stationary guide vane means located at said cover end andinternally of said container disposed to substantially redirect therotational component of flow in a direction to extract a substantialpart of the rotational component of the flow of materials passingtherethrough, the diameter of the wall at the cover end of saidcontainer being at least equal to the diameter of the wall at the baseend and the axial length of the container exceeding its maximumdiameter.

7. Stirring apparatus according to claim 6, said liquid driving unitcomprising a shaft extending through said base and drive connected tosaid impeller means.

8. Stirring apparatus according to claim 6, said liquid driving unitcomprising a shaft extending through said cover and drive connected tosaid impeller means.

9. Stirring apparatus according to claim 6, wherein said guide meansincludes a plurality of fixed vanes which are radial sheet-metalsections.

10. Stirring apparatus accordingto claim 6, wherein said stationaryguide vane means includes a ring-like member and a plurality of fixedguide vanes extending radially from said ring-like member.

11. Stirring apparatus according to claim 6, wherein said impeller meanscomprises a supporting shell spaced from but closely adjacent said baseand'said plurality of blades is fixed to said shell, said shell havingaperture means through which liquid may pass to flush out the spacebetween said shell and said base.

12. Stirring apparatus according to claiml 1, said impeller meansincluding a cover guide ring having an inlet opening for said impellermeans, said blades being disposed between said cover guide ring and saidshell.

13. Stirring apparatus according to claim 6, wherein the diameter of thecover end of said container is greater than the diameter of the baseend, and the wall of the container is frusto-conical in shape.

v 14. Stirring apparatus according to claim 13, wherein the diameter ofthe cover end of said container is approximately twice the diameter ofthe base end, and the axial length of the container is approximately 156 to 2 times the largest diameter of the container.

15. Stirring apparatus according to claim 6, the container iscylindrical and the ratio of its length to its diameter is greater than1:1;

16. Stirring apparatus according to claim 15, wherein the ratio of thelength of the container to its diameter is preferably 1 .4-l .8: l.

17. Stirring apparatus accordingto claim 6, wherein the container baseand cover a're'curved to provide a smooth flow path direction change atboth ends.

18. Stirring apparatus according to claim 6, wherein 1 UNITED S ATESPATENT OFFICE CERTIFICATE OF CORRECTION.

Patent No. 3,685,806 Dated Aug. 22, 1972 Inventor) Fritz Schoppe It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, line 27, after "aforesaid" insert tubulence spectrum in theknow stirring apparatus Column 5, line 6, change "i.e." (firstoccurrence) to occurs Column 7, line 51, change "not" to now Column 9,line 31, after "flange" insert rings Signed and sealed this 30th day ofJanuary 1973.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOT'ISCHALK Attesting Officer Commissionerof Patents 0.5, GO ERNMENT PR NTING OFFICE Hi9 0-366-334 UNITED STATESPATENT OEFICE CERTIFICATE OF CORRECTION Patent NO. 3,685,806 DatedAugust 22', 1972 Inventor(s) Fritz SChOppe it is certified that errorappears in the above-identified patentand that said Letters Patent arehereby corrected as shown below:

Column 3, line 27, after "aforesaid", insert turbulence spectrum in theknown stirring apparatus Column 5, line 6, change "i.e." (firstoccurrence) to occurs Column 7', line 51, changef'not" to now Column 9,line Z51, after "flange", insert rings This certificate supersedesCertificate of Correction issued Januar 30, 1973".

Signed and sealedth'islst day of'January 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Y jRENE D., TEGTMEYER Attesting Officer v ActingCommissioner of Patents USCOMM-DC compeg FORM Po-mso (10-69) a as.eovsnunzm nglygnue d nes =0" o-a e-Jgr,

1. A method of mixing a liquid material with another material, such aSanother liquid, a gas, or a particulate solid, in a container in whichthe materials are circulated between a first end of the container and asecond end of the container, the diameter of the second end being atleast equal to the diameter of the first end, comprising: imparting tothe materials within the container and at the first container end alimited throughflow with a peripheral spin component and having amaximum negative pressure at the center of the first end of thecontainer so as to produce an outer flow path zone of materials rotatingalong the inside surface of the wall of the container from the first endto the second end of the container, extracting a substantial part of thespin from the outer zone of flow at the second end providing asubstantially straight non-spinning flow to produce a higher staticpressure at the center of the second end than said maximum negativepressure at the center of the first end, thereby establishing an innerflow path of materials within said outer zone passing from said secondend to said first end which is substantially parallel to the outer zoneof flow, the interface between the opposite flow paths creating anannular turbulent elongate zone of mixing of the materials.
 2. A methodaccording to claim 1, wherein the inner flow path extends over asufficiently long distance of at least five times the thickness of eachindividual flow layer adjacent the longitudinal axis of the container,and the velocity of said inner flow is of equal order of magnitude butof opposite direction to the velocity of the outer zone of flow.
 3. Themethod according to claim 2, wherein the inner flow extends over adistance of about ten to twelve times the thickness of each individualflow layer in the region of the longitudinal axis of the container. 4.The method according to claim 1, wherein the diameter of the secondcontainer end is greater than the diameter of the first container endand the outer zone of flow of materials moves in a conically wideningpath from the first end to the second end.
 5. A method according toclaim 1, wherein material from the inner flow is sucked into the inletopening of a rotating centrifugal-type pump impeller disposed centrallywithin said container adjacent said first end, the impeller impartingthe limited throughflow and peripheral component to the materials todevelop the outer flow of material adjacent the wall of the container.6. Stirring apparatus for mixing a liquid material with another materialsuch as another liquid, a gas, or a finely divided solid, comprising: acontainer of circular transverse cross-section having a base at one endand a cover at its other end; and a liquid and material driving unitincluding a rotating impeller means positioned closely adjacent saidbase end; said impeller means having blade support means and a pluralityof radially directed blade means secured to said blade support means,said blade means having outlet portions disposed in a direction awayfrom said base end and with said support means enabling flow of materialleaving said impeller means, when rotating, to flow outward at the baseend and directed toward and along the adjoining container wall towardsaid other end while providing a rotational component in the flow pathalong the container wall, and stationary guide vane means located atsaid cover end and internally of said container disposed tosubstantially redirect the rotational component of flow in a directionto extract a substantial part of the rotational component of the flow ofmaterials passing therethrough, the diameter of the wall at the coverend of said container being at least equal to the diameter of the wallat the base end and the axial length of the container exceeding itsmaximum diameter.
 7. Stirring apparatus according to claim 6, saidliquid driving unit comprising a shaft extending through said base anddrive connected to said impeller means.
 8. Stirring apparatus accordingto claim 6, said liquid driving unit comprising a shaft extenDingthrough said cover and drive connected to said impeller means. 9.Stirring apparatus according to claim 6, wherein said guide meansincludes a plurality of fixed vanes which are radial sheet-metalsections.
 10. Stirring apparatus according to claim 6, wherein saidstationary guide vane means includes a ring-like member and a pluralityof fixed guide vanes extending radially from said ring-like member. 11.Stirring apparatus according to claim 6, wherein said impeller meanscomprises a supporting shell spaced from but closely adjacent said baseand said plurality of blades is fixed to said shell, said shell havingaperture means through which liquid may pass to flush out the spacebetween said shell and said base.
 12. Stirring apparatus according toclaim 11, said impeller means including a cover guide ring having aninlet opening for said impeller means, said blades being disposedbetween said cover guide ring and said shell.
 13. Stirring apparatusaccording to claim 6, wherein the diameter of the cover end of saidcontainer is greater than the diameter of the base end, and the wall ofthe container is frusto-conical in shape.
 14. Stirring apparatusaccording to claim 13, wherein the diameter of the cover end of saidcontainer is approximately twice the diameter of the base end, and theaxial length of the container is approximately 1 1/2 to 2 times thelargest diameter of the container.
 15. Stirring apparatus according toclaim 6, the container is cylindrical and the ratio of its length to itsdiameter is greater than 1:1.
 16. Stirring apparatus according to claim15, wherein the ratio of the length of the container to its diameter ispreferably 1.4-1.8:1.
 17. Stirring apparatus according to claim 6,wherein the container base and cover are curved to provide a smooth flowpath direction change at both ends.
 18. Stirring apparatus according toclaim 6, wherein the inner contour of the container comprises at leastone conical part and one cylindrical part.
 19. Stirring apparatusaccording to claim 6, wherein said driving unit comprises a rotatingcentrifugal pump-like impeller located adjacent said base end with itsaxial inlet positioned substantially coaxial with the longitudinal axisof said container and its radial outlet from its radially directedblades adapted to discharged a spinning flow of materials in an outerannular zone along the container wall from said base end to said coverend.